1. Technical Field
The present invention relates to an encoding device and a decoding device which detect falsification of a document.
2. Related Art
A document is required to be in a form which can be easily handled by a user so that it is suitably compressed while holding viewability to the extent that the contents of the document can be checked. On the other hand, falsification of a document including company information and private information is required to be prevented. For this reason, considerable attention is paid to coping with both viewability and falsification prevention.
Japanese Published Unexamined Patent Application No. 2001-094804 discloses a method of removing any unnecessary image portion such as background color or offset from a color input image while preventing the image from being deteriorated.
Japanese Published Unexamined Patent Application No. 2002-354253 discloses a method of removing a background without leaving any isolate point when the background is in a halftone dot range.
In any of these methods, however, falsification detection has not been considered.
Japanese Published Unexamined Patent Application No. Hei 11-338780 discloses a method of authenticating an electronic document provided by a user using an encryption function to make a document finger print.
However, a background portion necessary for falsification detection encoded at high compressibility disappears easily.